Tubular light sources, such as fluorescent lamps, typically provide a generally uniform cylindrical radiation pattern. The inside surface of the lamp envelope is coated with a phosphor material. For some applications, such as photocopy machine printing and liquid crystal display backlighting, a higher brightness than is normally delivered by a conventional fluorescent lamp, is required. The light emitted by a fluorescent lamp can be directed in a preferred direction by scraping away the phosphor coating and any reflective coating along a narrow strip extending the length of the lamp envelope to create an aperture.
Examples of aperture fluorescent lamps are disclosed in U.S. Pat. No. 3,225,241 issued Dec. 21, 1965 to Spencer et al, U.S. Pat. No. 3,987,331 issued Oct. 19, 1976 to Schreurs, U.S. Pat. No. 3,012,168 issued Dec. 5, 1961 to Ray et al, U.S. Pat. No. 3,275,872 issued Sep. 27, 1966 to Chernin et al, U.S. Pat. No. 3,115,309 issued Dec. 24, 1963 to Spencer et al, U.S. Pat. No. 3,067,351 issued Dec. 4, 1962 to Gungle et al and U.S. Pat. No. 3,717,781 issued Feb. 20, 1973 to Sadoski et al.
In the case of relatively large diameter fluorescent lamps, the aperture in the coating can be made using a scraper attached to the end of a rigid rod. As the scraper is pushed through the glass tube, radial pressure is applied to the rigid rod to keep the scraper in contact with the inside surface of the glass tube. The steel rod is of sufficient diameter to resist bending as the scraper is pushed through the glass tube.
In the case of relatively small diameter fluorescent lamps, i.e., those having a diameter of less than 1/2 inch, it is difficult to remove the phosphor coating from the inside surface of the lamp envelope to create an aperture. A miniature fluorescent lamp typically has an inside diameter in the range of about 3.75 mm to 5.75 mm. The overall length typically ranges from 4 to 20 inches. Due to the small inside diameter and the relatively long length, it is generally difficult to use the same scraping method and apparatus that are used for the larger diameter lamps. In particular, due to the vary small diameter required of any rod used to direct a scraper through the small diameter glass tube, it has been difficult to hold the scraper securely against the inside surface of the lamp to create an aperture because the rod tends to bend. Due to the difficulty of maintaining contact between the scraper and the inside lamp surface, multiple passes are required to remove all of the coating from a predetermined aperture. Multiple passes through the lamp increase the likelihood that the aperture will have a nonuniform width. Furthermore, the phosphor material is often abrasive in nature, and lamp envelopes have varying diameters due to manufacturing tolerances. Therefore, although a soft scraper is required to conform to diameter variations, the scraper must be sufficiently hard to resist the abrasive characteristics of the phosphor coating. A scraping tool for removing a coating from the inside surface of a lamp is disclosed in U.S. Pat. No. 2,362,384 issued Nov. 7, 1944 to Libby.
It is an object of the present invention to provide improved methods and apparatus for removing a predetermined area of phosphor coating and any reflective coating from the inside surface of a lamp envelope to provide an optical aperture.
Another object of the invention is to provide methods and apparatus for manufacturing aperture lamps wherein coatings are uniformly removed from the inside surface of the lamp envelope.
Still another object of the present invention is to provide methods and apparatus for making aperture lamps wherein apertures are manufactured faster and with more uniform results than in the prior art.
A further object of the invention is to provide methods and apparatus for making aperture lamps wherein removal of the coating from the inside surface of the lamp envelope is accomplished using fewer passes of the scraping tool through the lamp envelope.